Mobility Signaling Using Direct Or Indirect Signaling Based On Cell Residency Heuristics

ABSTRACT

A mobility signaling method and apparatus are disclosed. Mobility signaling is performed by, first, generating a mobility signaling message ( 300, 302 ) at a mobile node ( 100 ) to be sent to a correspondent node ( 112 ). Next, either direct signaling or indirect signaling is selected as a signaling mechanism for the mobility signaling message ( 300, 302 ) based on a cell residence heuristic. The mobility signaling message ( 300, 302 ) is then sent to the correspondent node using the selected signaling mechanism for the mobility signaling message ( 300, 302 ).

FIELD OF THE INVENTION

The present invention relates to mobility management schemes for usewith network communication systems and, more particularly, to mobilitysignaling methods for use in such systems.

BACKGROUND OF THE INVENTION

Mobility management schemes provide home/host and location mapping formobile devices (herein mobile nodes) that connect to a network, such asa global information network, e.g., the Internet. The network may bemade up of, for example, multiple Ethernet segments and wireless LANcells. The location of a mobile node within the network may changefrequently. For example, a mobile node may move within the networkbetween wireless LAN cells or from a wireless LAN cell to an Ethernetsegment. Mobility management schemes allow communication with the mobilenode regardless of its location. One such scheme is Mobile IPv6. Supportfor mobile nodes under Mobile IPv6 is described in Internet Request forComments (RFC) 3775 entitled “Mobility Support in IPv6” (referred toherein as RFC 3775).

A mobile node (MN) is associated with a home address (HADDR). The HADDRrepresents a home link/connection point to the network through which theMN can be reached regardless of its current point of attachment to thenetwork. While moving about the network, the MN may also be associatedwith a care-of address (COA). The COA represents a foreignlink/connection point to the network through which the MN may becurrently reached directly.

The MN registers its COA with a home agent (HA), a router accessible atthe home link of the MN. The HA keeps binding information for the MNthat includes the HADDR and the COA of the MN. The HA may interceptincoming packets addressed to the HADDR of the MN and forward theintercepted packets to the current location of the MN using the COA ofthe MN.

A MN may communicate with one or more correspondent nodes (CN), e.g.,other MNs. As with the MN, the location of each CN may changefrequently. Mobile IPv6 provides means for managing handover situationswhere both the MN and a CN with which the MN is communicating aremobile, such as when the MN and/or the CN change LAN cells. As part ofthe handover procedure, binding signaling is performed.

In RFC 3775, binding signaling includes performing a return routability(RR) procedure and a binding update (BU) procedure. The returnroutability procedure enables the CN to obtain some reasonable assurancethat the MN is in fact addressable at its claimed COA as well as at itsHADDR. With this assurance, the CN will accept binding updates from theMN that instruct the CN to direct data to the MN at its claimed COA.

The RFC 3775 return routability procedure involves a home test and acare-of test. During the home test, the MN forwards a packet to its HA,the HA for the MN receives and forwards the packet to the CN at itsHADDR, and an HA for the CN receives and forwards the packet to the CNat its COA. The CN then responds to the home test through the same path.During the care-of test, the MN transmits a packet to the HADDR of theCN and the HA for the CN receives and forwards the packet to the CN atits COA. The CN then responds to the care-of test through the same path.

An MN that is able to prove it is reachable at both its HADDR and itsCOA is authorized to perform the BU procedure. During the BU procedure,the MN transmits a packet containing a message to the HADDR of the CNand the HA for the CN receives and forwards the packet to the CN at itsCOA. The information in this message updates the address binding stateof the CN so that it may send packets directly to the MN's COA.

The combination of signaling for the return routability procedure (or analternative authorization procedure that proves to the CN that the MN isreachable at both the HADDR and the COA of the MN) and signaling for thebinding update procedure are termed “mobility signaling” in thisdocument. Such signaling introduces delays in handoff time.

SUMMARY OF THE INVENTION

Various aspects of the present invention are embodied in mobilitysignaling methods and apparatus. Mobility signaling is performed by,first, generating a mobility signaling message at a mobile node to besent to a correspondent node. Next, either direct signaling or indirectsignaling is selected as a signaling mechanism for the mobilitysignaling message based on a cell residency heuristic. The mobilitysignaling message is then sent to the correspondent node using theselected signaling mechanism for the mobility signaling message.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1 is a flow diagram illustrating a prior art data transmissionscheme for transmitting data packets between a mobile node and acorrespondent node;

FIG. 2 is a flow diagram illustrating a prior art mobility signalingscheme;

FIG. 3 is a flow diagram illustration a mobility signaling scheme inaccordance with an aspect of the present invention;

FIG. 4A is a flowchart of exemplary steps for performing home testmobility signaling in accordance with an aspect of the presentinvention;

FIG. 4B is a flowchart of exemplary steps for performing care-of testmobility signaling in accordance with an aspect of the presentinvention;

FIG. 4C is a flowchart of exemplary steps for performing binding updatemobility signaling in accordance with an aspect of the presentinvention;

FIG. 5 is a flowchart of exemplary steps for selecting indirect/directmobility signaling using an exemplary heuristic in accordance with anaspect of the present invention; and

FIG. 6 is a flowchart of exemplary steps for estimating a cell residencetime in accordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a mobile node (MN) 100 in communication with acorrespondent node (CN) 112 over a network. The MN 100 is associatedwith a home address (HADDR) 106 that represents a home link for the MN100 on the network and may also be associated with a care-of address(COA) 102 that represent a foreign link for the MN 100 on the networkwhen MN 100 is connected to the network at a point other than its homelink. Likewise, the CN 112 is associated with a HADDR 110 and may beassociated with a COA 114.

A home agent (HA) 104 is associated with the MN 100 and another homeagent (HA) 108 is associated with the CN 112. The HA 104 for the MN 100is a router located at the home link of the MN 100 and the HA 108 forthe CN 112 is a router located at the home link of the CN 112. The HA104 for the MN 100 stores the HADDR 106 and the COA 102 of the MN 100and the HA 108 for the CN 112 stores the HADDR 110 and the COA 114 ofthe CN 112. In use, the HA 104 for the MN 100 intercepts messagestransmitted to the HADDR 106 of the MN 100 when the MN 100 is away fromits home link and transfers the intercepted messages to the MN 100 usingthe COA 102 of the MN 100. Likewise, the HA 108 for the CN 112intercepts messages transmitted to the HADDR 110 of the CN 112 when theCN 112 is away from its home link and transfers the intercepted messagesto the CN 112 using the COA 114 of the CN 112.

The MN 100 includes a binding cache 103 that may store bindinginformation for one or more correspondent nodes, e.g., the CN 112. In anexemplary embodiment, the binding information includes a HADDR and a COAfor each correspondent node with which the MN 100 is in communication.For example, the binding cache 103 of the MN 100 may store the HADDR 110and the COA 114 of the CN 112. Likewise, the CN 112 includes a bindingcache 113 that may store binding information for the MN 100, e.g., theHADDR 106 and the COA 102 of the MN 100.

The MN 100 may communicate with the CN 112 using either an indirect path117 or a route-optimized/direct path 118. Data packets are routinelysent via the indirect path 117. The MN 100, for example, may send a datapacket to the CN 112 indirectly by addressing the packet to the HADDR110 of the CN 112. In accordance with this example, the data packet fromthe MN 100 is tunneled to the HA 104 of the MN 100. The data packet nexttakes an overlaid path 116 between the HA 104 of the MN 100 and the HA108 of the CN 112. The data packet is then tunneled from the HA 108 ofthe CN 112 to the CN 112 using the COA 114 of the CN 112.

Similarly, the CN 112 may send a data packet to the MN 100 indirectly byaddressing the packet to the HADDR 106 of the MN 100. In accordance withthis example, the data packet is tunneled from the CN 112 to the HA 108of the CN 112. The packet next takes the overlaid path 116 from the HA108 of the CN 112 to the HA 104 of the MN 100. The packet is thentunneled from the HA 104 of the MN 100 to the MN 100 using the COA 102of the MN 100.

Data packets may also be sent via the direct path 118. Typically, thepackets may be sent via the direct path 118 in accordance with aroute-optimization procedure. A data packet being sent directly from MN100 to CN 112 uses the COA 114 of the CN 112. The data packet may thusbe sent directly from the MN 100 to the CN 112, thereby bypassing the HA104 of the MN 100 and the HA 108 of the CN 112. Similarly, a data packetsent from the CN 112 to the MN 100 using the direct path 117 uses theCOA 102 of the MN 100 to send the packet directly from the CN 112 to theMN 100, thereby bypassing the HAs 104 and 108.

Route-optimization reduces the delay for transferring packets betweenthe MN 100 and the CN 112 by reducing per-packet overhead, therebyreducing transmission latencies. In order to utilize route-optimization,the MN 100 typically updates the CNs, e.g., the CN 112, with its bindinginformation (e.g., the HADDR 106 and the COA 102 of the MN 100), andvice versa. In addition, the MN and the CNs typically continue toprovide binding information (e.g., its HADDR and COA) through bindingupdates each time they change cells.

Mobility signaling is performed prior to establishingroute-optimization. In Mobile IPv6, the mobility signaling includes areturn routability procedure and a binding update procedure that areperformed before route-optimization may be established. Althoughmobility signaling is described below with reference to Mobile IPv6,this is to facilitate description and one of skill in the art willrecognize that the scope of the present invention encompasses othertypes of mobility signaling schemes.

The return routability procedure is performed prior to the bindingupdate procedure. During the return routability procedure the CN 112 isassured (e.g., through authentication) that the MN 100 is authorized touse the HADDR 106 and the COA 102 of the MN 100. During the bindingupdate procedure, the MN 100 provides the CN 112 with its bindinginformation (e.g., the HADDR 106 and the COA 102 of the MN 100), whichthe CN 112 stores in its binding cache 113 for use during subsequentdata packet transmissions. Similarly, the MN 100 is assured that the CN112 is authorized to use the HADDR 110 and the COA 114 of the CN 112using the return routability procedure. The CN 112 then provides the MN100 with its binding information (e.g., the HADDR 110 and the COA 114 ofthe CN 112) using the binding update procedure, which the MN 100 storesin its binding cache 103 for use during subsequent data packettransmissions.

Although Mobile IPv6 allows route-optimized data transmission, itrequires that mobility signaling initiated by the MN 100 use the HADDR110 of the CN 112 (and, thus, the HA 108 of the CN 112). Likewise,Mobile IPv6 requires that mobility signaling initiated by the CN 112 usethe HADDR 106 of the MN 100 (and, thus, the HA 104 of the MN 100).Accordingly, all mobility signaling for MN initiated signaling must berouted to the CN 112 via the HA 108 of the CN 112 and all mobilitysignaling for CN initiated signaling must be routed to the MN 100 viathe HA 104 of the MN 100.

FIGS. 2 and 3 are used to describe the return routability procedure andthe binding update procedure between the MN 100 and the CN 112 forconventional mobility signaling and for exemplary mobility signaling inaccordance with an aspect of the present invention, respectively. Thereturn routability procedure includes a Home Test Initiate (HoTi)message, a Home Test (HoT) message, a Care-of Test Initiate (CoTi)message, and a Care-of Test (CoT) message. For example, in a returnroutability procedure initiated by the MN 100, the MN 100 sends HoTi andCoTi messages to the CN 112. In response, the CN 112 sends a Home Test(HoT) message and a Care-of Test (CoT) message to the MN 100. Aftersuccessfully completing/satisfying the return routability procedure, theMN 100 generates a binding update (BU) message with an authenticationkey generated from key-tokens present in the HoT and CoT messages (whichincludes the HAADR 106 and the COA 102 of the MN 100) and sends the BUmessage to the CN 112, which updates its binding cache 113 with theHAADR 106 and the COA 102 of the MN 100. Similar signaling occurs for areturn routability procedure initiated by the CN 112.

In FIG. 2, in accordance with the conventional signaling protocol ofMobile IPv6, all mobility signaling messages are routed using anindirect signaling mechanism between the MN 100 and the CN 112 via theHA 108 for the CN 112 for mobility signaling initiated by the MN 100.For example, the HoTi message is transferred from the MN 100 throughboth of the HAs 104/108 to the CN 112 (with the HoT message beingreturned along the same path) and the CoTi and BU messages aretransferred from the MN 100 to the CN 112 through the HA 108 (with theCoT message being returned along the same path). Thus, all mobilitysignaling messages for mobility signaling initiated by the MN 100 travelthrough the HA 108 of the CN 112, which introduces delay to the mobilitysignaling. Similarly, all mobility signaling messages for mobilitysignaling initiated by the CN 112 travel through the HA 104 of the MN100, which also introduces delay to the mobility signaling.

In FIG. 3, in accordance with an exemplary aspect of the presentinvention, all mobility signaling messages are routed using a directsignaling mechanism between the MN 100 and the CN 112 for mobilitysignaling initiated by the MN 100. For example, the HoTi message istransferred from the MN 100 through only the HA 104 of the MN 100 (asopposed to both of the HAs 104/108 for indirect signaling mechanisms)and then directly to the CN 112 (with the HoT message being returnedalong the same path) and the CoTi/BU messages are transferred from theMN 100 directly to the CN 112 without passing through either of the HA104/108 (with the CoT message being returned along the same path). Thus,all mobility signaling messages for mobility signaling initiated by theMN 100 bypass the HA 108 for the CN 112, thereby removing delay from themobility signaling. Similarly, all mobility signaling messages formobility signaling initiated by the CN 112 bypass the HA 104 for the MN100, thereby also removing delay from the mobility signaling.

FIGS. 4A through 4C depict flow charts of exemplary mobility signalingsteps in accordance with aspects of the present invention. The exemplarysteps are described below with reference to FIGS. 2 and 3.

FIG. 4A depicts a flow chart 400 of exemplary steps for sending a HoTimessage from a MN 100 to a CN 112 during a return routability procedureaccording to an aspect of the present invention. At block 402, the MN100 generates the HoTi message, which includes the HADDR 106 of the MN100.

At block 404, in accordance with an exemplary embodiment, the MN 100selects an indirect signaling mechanism (see FIG. 2) or a directsignaling mechanism (see FIG. 3) as the signaling mechanism for the HoTimessage. In an exemplary embodiment, the selection of the signalingmechanism is based on a cell residency heuristic, which is described indetail below. If the heuristic indicates indirect signaling, processingproceeds at block 408 after the HoTi is tunneled to the HA 104 for theMN 100 with the HADDR 110 of the CN 112 as the destination at block 406.Otherwise, if the heuristic indicates direct signaling, processingproceeds at block 412 after the HoTi is tunneled to the HA 104 for theMN 100 with the COA 114 of the CN 112 as the destination at block 406′.

At block 408, the HA 104 for the MN 100 routes the HoTi message to theHADDR 110 of the CN 112 where it is intercepted by the HA 108 for the CN112. Then, at block 410, the HA 108 for the CN 112 tunnels the HoTimessage to the CN 112 using the COA 114 of the CN 112. Thus, the HoTimessage passes through the HA 108 for the CN 112, which introduces delayas the HoTi message travels from the MN 100 to the CN 112.

At block 412, the HA 104 routes the HoTi message directly to the CN 112using the COA 114 of the CN 112. Thus, the HoTi message bypasses the HA108 for the CN 112, which eliminates the delay that would be introducedto the HoTi message as it travels from the MN 100 to the CN 112 using anindirect signaling mechanism.

Although not shown, a HoT message from the CN 112 that is generated inresponse to receipt of the HoTi message from the MN 100 may travel fromthe CN 112 to the MN 100 using the same signaling mechanism selected instep 404. Alternatively, the same (or a different heuristic) may beapplied by the CN 112 and/or HA 108 in determining whether the HoTmessage should use the indirect signaling mechanism or the directsignaling mechanism.

FIG. 4B depicts a flow chart 415 of exemplary steps for sending a CoTimessage from a MN 100 to a CN 112 during a return routability procedureaccording to an aspect of the present invention. At block 418, the MN100 generates the CoTi message, which includes the COA 102 of the MN100. At block 404′, the MN 100 selects an indirect signaling mechanism(see FIG. 2) or a direct signaling mechanism (see FIG. 3) as thesignaling mechanism for the CoTi message. In an exemplary embodiment,the selection of the signaling mechanism is based on a cell residencyheuristic, which is described in detail below. If the heuristicindicates indirect signaling, processing proceeds at block 420.Otherwise, if the heuristic indicates direct signaling, processingproceeds at block 424.

At block 420, the MN 100 transmits the CoTi message to the HADDR 110 ofthe CN 112 where it is intercepted by the HA 108 for the CN 112. Then,at block 422, the HA 108 for the CN 112 tunnels the CoTi message to theCN 112 using the COA 114 of the CN 112. Thus, the CoTi message passesthrough the HA 108 for the CN 112, which introduces delay as the CoTimessage travels from the MN 100 to the CN 112.

At block 424, the MN 100 transmits the CoTi message directly to the CN112 using the COA 114 of the CN 112. Thus, the CoTi message bypasses theHA 108 for the CN 112, which eliminates the delay that would beintroduced to the CoTi message as it travels from the MN 100 to the CN112 using an indirect signaling mechanism.

Although not shown, a CoT message from the CN 112 that is generated inresponse to receipt of the HoTi message from the MN 100 may travel fromthe CN 112 to the MN 100 using the same signaling mechanism selected instep 404′, e.g., based on a cell residency heuristic. Alternatively, thesame (or a different heuristic) may be applied by the CN 112 indetermining whether the CoT message should use the indirect signalingmechanism or the direct signaling mechanism.

FIG. 4C depicts a flow chart 450 of exemplary steps for sending abinding update (BU) message from a MN 100 to a CN 112 during a bindingupdate procedure according to an aspect of the present invention. In anexemplary embodiment, the binding update procedure is performed afterthe HoT message and the CoT message, which are responsive to the HoTimessage and the CoTi message, respectively, are received by the MN 100in accordance with the return routability procedure.

At block 426, the MN 100 processes the HoTi, HoT, CoTi, and CoT messagesfor a return routability procedure initiated by the MN 100. At block428, the MN 100 generates a binding update (BU) message based at leastin part on information obtained from processing the HoTi, HoT, CoTi, andCoT messages.

At block 430, a decision is made regarding the CoTi and CoT messages. Ifthe CoT message was received in response to a CoTi message that wastransmitted from the MN 100 to the CN 112 using a direct signalingmechanism (rather than an indirect signaling mechanism), processingproceeds at block 404″. Otherwise, processing proceeds at block 440.

At block 404″, the MN 100 selects an indirect signaling mechanism (seeFIG. 2) or a direct signaling mechanism (see FIG. 3) as the signalingmechanism for the BU message. In an exemplary embodiment, the selectionof the signaling mechanism is based on a cell residency heuristic, whichis described in detail below. If the heuristic indicates indirectsignaling, processing proceeds at block 440. Otherwise, if the heuristicindicates direct signaling, processing proceeds at block 444.

At block 440, the MN 100 transmits the BU message to the HADDR 110 ofthe CN 112 where it is intercepted by the HA 108 for the CN 112. Then,at block 442, the HA 108 for the CN 112 tunnels the BU message to the CN112 using the COA 114 of the CN 112. Thus, the BU message passes throughthe HA 108 for the CN 112, which introduces delay as the BU messagetravels from the MN 100 to the CN 112.

At block 444, the MN 100 transmits the BU message directly to the CN 112using the COA 114 of the CN 112. Thus, the BU message bypasses the HA108 for the CN 112, which eliminates the delay that would be introducedto the BU message as it travels from the MN 100 to the CN 112 using anindirect signaling mechanism.

FIG. 5 depicts a flow chart 500 of exemplary steps for selecting eitheran indirect signaling mechanism or a direct signaling mechanism based onan exemplary heuristic, e.g., steps 404, 404′, and 404″ of FIGS. 4A, 4B,and 4C, respectively. In an exemplary embodiment, the heuristic is basedon an estimated cell residence time of the CN 112 (e.g., the amount ofthe time the CN 112 is likely to remain attached to the current cell),which is discussed below with reference to FIG. 6. Using the estimatedcell residence time, the exemplary heuristic measure desirablycalculates whether it is likely that the CN 112 is going to leave itscurrent cell before an operation associated with a mobility signalingmessage operation reaches the CN 112 (e.g., a return routabilityprocedure or binding update message from the MN 100). If it isdetermined that the CN 112 is unlikely to move to another cell duringthe transmission of a message by the MN 100 (e.g., HoTi, CoTi, or BUmessages) and, optionally, a corresponding reply message (e.g., HoT andCot messages), the HA 108 for the CN 112 may desirably be bypassedcompletely, thus a direct signaling mechanism is employed. Otherwise anindirect signaling mechanism may be employed.

At block 502, the MN 100 determines an estimated cell residence time forthe CN 112. The estimated cell residence time represents the amount oftime the CN 112 is likely to remain at any given cell. Exemplary methodsfor determining the estimated cell residence time are described below.

At block 504, the MN 100 determines an elapsed cell residence time forthe CN 112 at a current cell. In an exemplary embodiment, the elapsedcell residence time is determined by calculating the difference betweena current time and a time corresponding to the receipt of the lastbinding update from the CN 112.

At block 506, the MN 100 determines a threshold value for mobilitysignaling with the CN 112. In an exemplary embodiment, the thresholdvalue is based on a determined value and a predetermined value. Forexample, the threshold value may be the sum of a calculated averagehandover delay and a predetermined cell residency threshold, e.g., 0.1seconds to 10 seconds. The calculation of an average handover delay willbe understood by one of ordinary skill in the art. In alternativeexemplary embodiments, the threshold value may be based solely ondetermined or predetermined values.

At block 508, a decision is made regarding the likelihood that the CN112 will remain attached to its current cell until a mobility signalingmessage operation is complete. If it is determined that the CN 112 willlikely remain attached to its current node, the direct signalingmechanism is selected. Alternatively, if it is determined that the CN112 will likely not remain attached to its current node, the indirectsignaling mechanism is selected. Additionally, if a mobility signalingmessage operation fails, e.g., due to problems with the wirelesschannel, the MN 100 may select the indirect signaling mechanism forretransmission.

In an exemplary embodiment, it will be determined that the CN 112 willlikely remain attached to its current node if the elapsed cell residencetime is less than about (e.g., less than/less than or equal to) theestimated cell residence time minus a threshold value. In accordancewith this embodiment, it will be determined that the CN 112 will likelynot remain attached to its current node if the elapsed cell residencetime is greater than about (e.g., greater than or equal to/greater than)the estimated cell residence time minus a threshold value.

FIG. 6 depicts a flow chart 600 of exemplary steps to determine anestimated cell residence time. At block 600, a prior actual BU timeparameter for a binding update message received by the MN 100 from theCN 112 and an estimated cell residence time parameter are initialized.These values may be actual parameters if the system has been running fora sufficient time to have actual values generated, or they may beinitial estimates if the system is just being initiated.

At block 602, the MN 100 receives a binding update message from the CN112. At block 604, the received BU message is compared against a priorBU message to determine if it is for a new binding having a new COA,indicating that the CN 112 has changed cells. If the BU message is notfor a new binding, the process returns to step 602 and waits for thenext BU. Otherwise, processing proceeds at block 606. It will beunderstood by one of skill in the art that if BU messages are sent onlywhen the CN 112 changes cells, the step of block 604 may be omitted.

At block 606, the MN 100 determines an actual cell residence time thatrepresents the amount of time the CN 112 was at a previousresidence/cell. In an exemplary embodiment, the actual cell residencetime is determined by calculating the difference between a previous BUtime of a previous binding update message and a current BU time for asuccessive binding update message.

At block 608, a new estimated cell residence time is determined. In anexemplary embodiment, the estimated cell residence time is determined byaveraging the actual cell residence time determined at block 606 and oneor more previously determined actual cell residence times. In anotherexemplary embodiment, a running average cell residence time ismaintained by averaging the actual prior cell residence time with apreviously calculated average. This average may be a weighted average,for example, to reduce/increase the relative contribution of the actualprior cell residence time to the average, e.g., the actual prior cellresidence time may receive a weight of 0.3 while the current averagevalue receives a weight of 0.7.

At block 610, the estimated cell residence time parameter is updatedusing the new estimated cell residence time determined in the step ofblock 608. At block 612, the prior BU time is updated with the currentBU time. The process returns to step 602 to wait for the next bindingupdate message from the CN 112.

In addition to the estimated cell residence time, an exemplary heuristicmay use factors such as the delay for message signaling. For example,the exemplary heuristic may determine a total delay for HoTi/HoT andCoTi/CoT messaging when using either direct or indirect messagesignaling. The signaling may be comprised of a series of relayedmessages passed between one of the four network entities: CN 112, MN 100or either of their HAs 108/104. RTT is the round trip time, e.g. for theHoTi/HoT pair or the CoTi/CoT pair. The maximum duration of either thehome and care-of tests may be added to the subsequent binding signalingpassing to the CN, which is relayed by the HA 104 for the CN 108.

For example, equation (1) represents the total delay for an indirectsignaling exchange, D^(indirect), between a MN 100 and its peer CN 112.$\begin{matrix}{D^{indirect} = {{\max\left( {{RTT}_{{MN} - {HA}_{MN}} + {RTT}_{{HA}_{MN} - {HA}_{CN}} + {{RTT}_{{{HA}_{CN} - {CN}},}{RTT}_{{MN} - {HA}_{CN}}} + {RTT}_{{HA}_{CN} - {CN}}} \right)} + T_{{MN}->{HA}_{CN}} + T_{{HA}_{CN}->{CN}}}} & (1)\end{matrix}$The first line represents the total HoTi/HoT messaging time in which around trip time (RTT) for the HoTi message to transfer from the MN 100to the HA 104 for the MN 100 and the HoT message to transfer from the HA104 for the MN 100 to the MN 100, a RTT for the HoTi message to transferfrom the HA 104 to the HA 108 for the CN 112 and the HoT message totransfer from the HA 108 to the HA 104, and a RTT for the HoTi messageto transfer from the HA 108 to the CN 112 and the HoT message totransfer from the CN 112 to the HA 108 are combined. The second linerepresent the total CoTi/CoT messaging time in which a round trip time(RTT) for the CoTi message to transfer from the MN 100 to the HA 108 forthe CN 112 and the CoT message to transfer from the HA 108 to the MN 100and a RTT for the CoTi message to transfer from the HA 108 to the CN 112and the CoT message to transfer from the CN 112 to the HA 108 arecombined. The third line represents the subsequent binding signaling tothe CN 112 in which the time for the binding message to transfer fromthe MN 100 to the HA 108 for the CN 112 and the time for the bindingmessage to transfer from the HA 108 to the CN 112 are combined.

Equation (2) represents the total delay for a direct signaling exchange,D^(direct), between a MN 100 and its peer CN 112. $\begin{matrix}{D^{direct} = {{\max\left( {{RTT}_{{MN} - {HA}_{MN}} + {{RTT}_{{HA}_{MN} - {CN}^{\prime}}{RTT}_{{MN} - {CN}}}} \right)} + T_{{MN}->{CN}}}} & (2)\end{matrix}$The first line represents the total HoTi/HoT messaging time in which aRTT for the HoTi message to transfer from the MN 100 to the HA 104 forthe MN 100 and the HoT message to transfer from the HA 104 for the MN100 to the MN 100 and a RTT for the HoTi message to transfer directlyfrom the HA 104 to the CN 112 and the HoT message to transfer directlyfrom the CN 112 to the HA 104 are combined. The second line representthe total CoTi/CoT messaging time in which a round trip time (RTT) forthe CoTi message to transfer directly from the MN 100 to the CN 112 andthe CoT message to transfer directly from the CN 112 to the MN 100. Thethird line represents the subsequent binding signaling to the CN 112 inwhich the time for the binding message to transfer directly from the MN100 to the CN 112 is determined.

If either the MN 100 or CN 112 is distant from its HA, it may bedesirable to bypass the HA 108 of the CN 112. If signaling latencies areimportant, such as when signaling is on the critical path of servicerestoration after movement, there may be a significant improvement insignaling delay if direct signaling is used.

Exemplary heuristics may further determine a probability of signalingloss, for example, by using a geometric relationship between a CN movingat some speed at some radius within a cell. The CN's position may beestimated using the distance the CN may travel, at a speed, to determinethe likelihood of the CN moving to another cell. Signaling lossprobabilities may be determined for the indirect signaling and directsignaling using geometric relationships.

Although the exemplary heuristic measure has been shown to include usingan estimated cell residence time, messaging delay and a probability ofsignaling loss, it is contemplated that other measures may be usedwithin the heuristic measure without limiting the scope of theinvention. For example, exemplary estimated cell residence time may usea probability distribution, such as a Gaussian distribution, or aweighted probability to determine the probability of a signaling loss.The estimated cell residence may be adaptively tracked and updated fromprior binding information to better predict the CN's estimated cellresidence time. Information such as service restoration requests mayalso be incorporated into the heuristic measure.

There are trade-offs for using direct and indirect signaling. A cost fordirect signaling may include, for example, a higher likelihood of amessage becoming lost and, thus, forcing a timeout and resend. A cost ofindirect signaling, for example, may include a delay caused by thelonger indirect route rather than the direct route. Other factors may beincluded in the indirect or direct costs without limiting the scope ofthe present invention. According to a method embodied in the presentinvention, a signaling mechanism may be chosen by a heuristic measure toreduce the delay of signaling between the MN and CN while maintainingpacket loss below an acceptable level. Thus, the delay involved in thereturn routability procedure may be reduced while maintaining acceptablepacket loss rates.

Although the invention has been described as a method, it iscontemplated that one or more of the above-described component,functions, and/or steps may be implemented through a software programthat controls a computer. The software program may be embodied in acomputer-readable carrier such as an integrated circuit, a memory card,a magnetic or optical disk or an audio-frequency, radio-frequency oroptical carrier wave.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

1. A mobility signaling method comprising the steps of: generating, at amobile node, a mobility signaling message to be sent to a correspondentnode; selecting either direct signaling or indirect signaling as asignaling mechanism for the mobility signaling message based on a cellresidency heuristic; and sending the mobility signaling message to thecorrespondent node using the selected signaling mechanism for themobility signaling message.
 2. The method of claim 1, wherein theselecting step comprises the steps of: determining an estimated cellresidence time for the correspondent node; determining an elapsed cellresidence time for the correspondent node at a current cell; determiningif the correspondent node is likely to remain at the current cell untilan operation associated with the mobility signaling message is completebased at least in part on the estimated cell residence time and theelapsed cell residence time; and selecting the direct signalingmechanism if the correspondent node is determined to likely remain atthe current cell and selecting the indirect signaling mechanism if thecorrespondent node is determined to likely not remain at the currentcell.
 3. The method of claim 2, wherein the step of determining if thecorrespondent node is likely to remain at the current cell is furtherbased on a threshold value and wherein the correspondent node isdetermined to likely remain at the current cell if the elapsed cellresidence time is less than about the estimated cell residence timeminus the threshold value and the correspondent node is determined tolikely not remain at the current cell if the elapsed cell residence timeis greater than about the estimated cell residence time minus thethreshold value.
 4. The method of claim 2, wherein the estimated cellresidence time is determined by averaging a plurality of previous actualcell residence times.
 5. The method of claim 4, wherein each actual cellresidence time is determined by calculating a difference betweensuccessive binding update messages received from the correspondent node.6. The method of claim 4, wherein the estimated cell residence time isfurther determined by weighting one or more of the previous actual cellresidence times.
 7. The method of claim 2, wherein the estimated cellresidence time is determined by calculating an average of an actualprior cell residence time with a previously calculated average.
 8. Themethod of claim 7, wherein the estimated cell residence time is furtherdetermined by weighting at least one of the actual prior cell residencetime or the previously calculated average.
 9. The method of claim 1,wherein the correspondent node has a home address and a care-of addressand wherein the sending step comprises the step of sending the mobilitysignaling message to the care-of address of the correspondent node whenthe direct signaling mechanism is selected as the signaling mechanism.10. The method of claim 9, wherein the sending step comprises the stepof sending the mobility signaling message to the home address of thecorrespondent node when the indirect signaling mechanism is selected asthe signaling mechanism.
 11. The method of claim 1, wherein the mobilitymessage is a home test init (HoTi) message and wherein the sending stepcomprises the steps of: for the indirect signaling mechanism: tunnelingthe HoTi message to a home agent of the mobile node; routing the HoTimessage from the home agent to an other home agent of the mobile node;and tunneling the HoTi message from the other home agent to thecorrespondent node; and for the direct signaling mechanism: tunnelingthe HoTi message to the home agent of the mobile node; and routing theHoTi message directly from the home agent to the correspondent node. 12.The method of claim 1, wherein the mobility message is a care-of init(CoTi) message and wherein the sending step comprises the steps of: forthe indirect signaling mechanism: transmitting the CoTi message from themobile node to a home agent of the correspondent node; and tunneling theCoTi message from the home agent to the correspondent node; and for thedirect signaling mechanism: transmitting the CoTi message from themobile node directly to the correspondent node.
 13. The method of claim1, wherein the mobility message is a binding update (BU) message andwherein the sending step comprises the steps of: for the indirectsignaling mechanism: transmitting the BU message from the mobile node toa home agent of the correspondent node; and tunneling the BU messagefrom the home agent to the correspondent node; and for the directsignaling mechanism: transmitting the BU message from the mobile nodedirectly to the correspondent node.
 14. The method of claim 1, whereinthe cell residency heuristic determines at least one of (a) aprobability of signaling loss or (b) a geometric relationship of thecorrespondent node within a cell.
 15. A mobility signaling apparatuscomprising: means for generating, at a mobile node, a mobility signalingmessage to be sent to a correspondent node; means for selecting eitherdirect signaling or indirect signaling as a signaling mechanism for themobility signaling message based on a cell residency heuristic; andmeans for sending the mobility signaling message to the correspondentnode using the selected signaling mechanism for the mobility signalingmessage.
 16. The apparatus of claim 15, wherein the correspondent nodehas a home address and a care-of address and wherein the sending meanssends the mobility signaling message to the care-of address of thecorrespondent node when the direct signaling mechanism is selected asthe signaling mechanism.
 17. The apparatus of claim 15, wherein themobility message is a home test init (HoTi) message and wherein thesending means comprises: for the indirect signaling mechanism: means fortunneling the HoTi message to a home agent of the mobile node; means forrouting the HoTi message from the home agent to an other home agent ofthe mobile node; and means for tunneling the HoTi message from the otherhome agent to the correspondent node; and for the direct signalingmechanism: means for tunneling the HoTi message to the home agent of themobile node; and means for routing the HoTi message from the home agentdirectly to the correspondent node.
 18. The apparatus of claim 15,wherein the mobility message is a care-of init (CoTi) message andwherein the sending means comprises: for the indirect signalingmechanism: means for transmitting the CoTi message from the mobile nodeto a home agent of the correspondent node; and means for tunneling theCoTi message from the home agent to the correspondent node; and for thedirect signaling mechanism: means for transmitting the CoTi message fromthe mobile node directly to the correspondent node.
 19. The apparatus ofclaim 15, wherein the mobility message is a binding update (BU) messageand wherein the sending means comprises: for the indirect signalingmechanism: means for transmitting the BU message from the mobile node toa home agent of the correspondent node; and means for tunneling the BUmessage from the home agent to the correspondent node; and for thedirect signaling mechanism: means for transmitting the BU message fromthe mobile node directly to the correspondent node.
 20. A computerreadable carrier including a computer program for configuring a computerto perform a mobility signaling method according to claim
 1. 21. Thecomputer readable carrier of claim 20, wherein the correspondent nodehas a home address and a care-of address and wherein the sending stepcomprises the step of sending the mobility signaling message to thecare-of address of the correspondent node when the direct signalingmechanism is selected as the signaling mechanism.
 22. The computerreadable carrier of claim 20, wherein the mobility message is a hometest init (HoTi) message and wherein the sending step comprises thesteps of: for the indirect signaling mechanism: tunneling the HoTimessage to a home agent of the mobile node; routing the HoTi messagefrom the home agent to an other home agent of the mobile node; andtunneling the HoTi message from the other home agent to thecorrespondent node; and for the direct signaling mechanism: tunnelingthe HoTi message to the home agent of the mobile node; and routing theHoTi message from the home agent directly to the correspondent node. 23.The computer readable carrier of claim 20, wherein the mobility messageis a care-of init (CoTi) message and wherein the sending step comprisesthe steps of: for the indirect signaling mechanism: transmitting theCoTi message from the mobile node to a home agent of the correspondentnode; and tunneling the CoTi message from the home agent to thecorrespondent node; and for the direct signaling mechanism: transmittingthe CoTi message from the mobile node directly to the correspondentnode.
 24. The computer readable carrier of claim 20, wherein themobility message is a binding update (BU) message and wherein thesending step comprises the steps of: for the indirect signalingmechanism: transmitting the BU message from the mobile node to a homeagent of the correspondent node; and tunneling the BU message from thehome agent to the correspondent node; and for the direct signalingmechanism: transmitting the BU message from the mobile node directly tothe correspondent node.